Water-based polyurethane dispersions
What they are, how they are classified, and why they are replacing solvent-based dispersions in industrial finishing.
The principle: water instead of solvent
Water-based polyurethanes use water as the dispersing medium and are therefore cleaner and safer to handle than the more widespread solvent-based polyurethane dispersions.
The polymer is not dissolved but dispersed in the aqueous phase as very fine particles. During drying the water evaporates and the particles coalesce, forming a continuous film on the treated surface.
How they are classified
According to the synthesis of the monomers, water-based polyurethane coatings can be divided into polyether, polyester or mixed bases. According to the type of diisocyanates used in their production they are classified as aliphatic or aromatic.
- Polyester — good mechanical properties and high adhesion on most substrates.
- Polyether — better hydrolysis resistance and improved flexibility at low temperatures.
- Polycarbonate — the highest resistance to hydrolysis and abrasion, for demanding applications.
- Aliphatic — colour stability over time, does not yellow on exposure to light.
- Aromatic — good mechanical performance at lower cost, with a tendency to discolour.
Where they are used
They can be used, for instance, for finishing or laminating many different materials: leather, paper, synthetic fibres and others. Polyurethane dispersions can form soft, rigid, matt, clear or gloss films; the range of characteristics that can be defined during synthesis is very wide.
Where a water base has limits
A water base is not the answer to every situation. Drying depends on temperature and humidity on the shop floor: in cold or very damp conditions water evaporates more slowly and cycle times get longer. The film only forms properly above the minimum film forming temperature (MFFT), which for all Aqua Polymers dispersions is below 20 °C according to 2026 laboratory analyses. Aromatic grades, which cost less, also tend to yellow on exposure to light: where colour must stay stable, aliphatic grades are needed.
What defines a dispersion
Water as the medium
No organic solvent to evaporate, recover or dispose of.
No free isocyanate
Safer handling for operators on the shop floor.
Low VOC
Reduced emissions of volatile organic compounds.
Acrylic compatibility
Fits into existing formulations without redesigning them.
Source: technical content prepared by the Aqua Polymers S.r.l. laboratory, Tromello (PV), Italy. · Last updated: September 2026.